1. Technical Field
The present invention relates to a semiconductor device including a diode.
2. Related Art
FIG. 7 is a cross-sectional view of a semiconductor device according to a related art. A vertical zener diode included in the semiconductor device is disclosed in US 2012/0074522 (FIG. 2).
The semiconductor device shown in FIG. 7 includes a silicon substrate 111, and an N-type buried layer 112 provided on the silicon substrate 111. A P-type epitaxial growth layer 113 is provided on the N-type buried layer 112, and field insulating films 116, 117, 118 and 119 made of LOCOS oxide films are provided on the P-type epitaxial growth layer 113.
A cathode 114 composed of an N−-type impurity region is provided in the P-type epitaxial growth layer 113 that is on the inner sides of the field insulating films 117 and 118, and the N−-type cathode 114 is electrically connected to the N-type buried layer 112. An anode 121 composed of a P+-type impurity region is provided on the cathode 114 provided in the P-type epitaxial growth layer 113 that is on the inner sides of the field insulating films 117 and 118. A PN junction of the zener diode is provided by the P+-type anode 121 and the cathode 114.
N+-type impurity regions 122 are provided respectively on the P-type epitaxial growth layer 113 at a position that is on the outer side of the field insulating film 117 and is on the inner side of a field insulating film 116, and on the P-type epitaxial growth layer 113 at a position that is on the outer side of the field insulating film 118 and is on the inner side of a field insulating film 119. In the P-type epitaxial growth layer 113, N−-type impurity regions 115 located under the N+-type impurity regions 122 are provided, and the N−-type impurity regions 115 are electrically connected to the N-type buried layer 112. A silicide film 123 is provided on the N+-type impurity regions 122 and the anode 121.
The above-described diode is problematic in that the breakdown voltage fluctuates if the diode is repeatedly used.